Digital cellular telecommunication systems meanwhile are in common use. One example for such a digital cellular telecommunication system is the pan-European mobile telecommunication network GSM for which technical specifications have been elaborated by the European Telecommunication Standards Institute ETSI. Digital cellular telecommunication systems allow its users to initiate and receive calls at any geographical area within the radio coverage of the Home Public Land Mobile Network HPLMN operated by the network operator selected by the subscriber and also within the radio coverage area of partners of the network operator providing services within the Home Public Land Mobile Network HPLMN, i.e. network operators having a roaming agreement with the HPLMN-network operator.
As is shown in FIG. 6, there are usually provided several levels of granularity for the location of information within the pan-European digital cellular telecommunication system. The GSM service area comprises a plurality of N Public Land Mobile Networks PLMN service areas wherein technically the usage of a mobile station is possible. Each Public Land Mobile Network PLMN service area is the domain of a single network operator and is itself divided into a plurality of M Mobile Services Switching Centre MSC service areas. Each Mobile Services Switching Centre MSC service area itself comprises on the average a plurality of K location areas that are constituted by a plurality of cells of which the number is P on the average. It should be noted that the borders of location areas do not necessarily match the borders of the Mobile Services Switching Centre MSC service areas. Also, the location areas represent the geographical areas wherein paging messages are broadcast to all subscribers currently visiting the respective location areas.
Basic sub-systems for the architecture of such a digital cellular telecommunication network system are to establish the services within a PLMN service area, i.e. a Base Station Sub-System BSS, a Network and Switching Sub-System NSS and an Operational Sub-System OSS. The Base Station Sub-System BSS provides and manages transmission paths between Mobile Stations MS and the Network and Switching Sub-System NSS. The Network and Switching Sub-System NSS manages communications and connections to Mobile Stations MS. Neither the Network and Switching Sub-System NSS nor the Base Station Sub-System BSS are in direct contact with external networks, e.g. a Public Switched Telephone Network PSTN, an Integrated Services Digital Network ISDN, or a Packet Switched Public Data Network PSPDN. While the Mobile Station MS, the Base Station Sub-System BSS, and the Network and Switching Sub-System NSS form the operational part of the digital cellular telecommunication network system, the Operational Sub-System OSS provides means for a service provider for their control.
Therefore, in a digital cellular telecommunication network system interaction between sub-systems can be grouped into two main parts, i.e. the operational part via the external networks/GSM service area to the Network and Switching Sub-System NSS, the Base Station Sub-System BSS, the Mobile Station MS to the user and the control part where the service provider directly accesses the Operational Sub-System OSS.
FIG. 7 shows components of the digital cellular telecommunication system being related to the Network and Switching Sub-System NSS and the Base Station Sub-System BSS and the Mobile Station MS, respectively. In particular, FIG. 7 shows a Public Land Mobile Network PLMN that may either be the Home Public Land Mobile Network HPLMN or the Visiting Public Land Mobile Network VPLMN of a subscriber.
To achieve a link between two different PLMN service areas there is provided a Gateway Mobile Service Switching Centre GMSC that serves to determine specific locations of a Mobile Station MS in the digital cellular telecommunication network system and to route calls towards a Mobile Station MS. In addition, an even more important task of the Gateway Mobile Service Switching Centre GMSC is to connect to other networks. For a GSM internal call no Gateway Mobile Service Switching Centre GMSC needs to be invoked.
The Gateway Mobile Service Switching Centre GMSC is connected to a functional unit called Home Location Register HLR wherein two types of information are stored: subscriber information and mobile information to allow incoming calls to be routed to the Mobile Station MS. Any administrative action by the network operator with respect to mobile station data is carried out in the Home Location Register HLR.
To route a call to a Mobile Station MS the Gateway Mobile Service Switching Centre GMSC is also connected to a Mobile Service Switching Centre MSC through which the Mobile Station MS can obtain a service. The Mobile Service Switching Centre MSC performs the necessary switching functions required for Mobile Stations MS covered by this Mobile Service Switching Centre MSC. Also, the Mobile Service Switching Centre MSC monitors the mobility of its Mobile Stations MS and manages necessary resources required to handle and update the location registration procedures.
As outlined above and shown in FIG. 7 the Public Land Mobile Network HPLMN/VPLMN comprises a plurality of Mobile Service Switching Centres MSC and respective service areas each covering a predetermined number of basic cells wherein a Mobile Station MS can move. To this end, each Mobile Service Switching Centre MSC is connected to a Visitor Location Register VLR. The Visitor Location Register VLR is a functional unit that dynamically stores mobile station information, such as the location area in case the mobile station is located in the service area covered by the Visitor Location Register VLR. When a roaming Mobile Station MS enters a service area assigned to a specific Mobile Service Switching Centre MSC the Mobile Service Switching Centre MSC informs the associated Visitor Location Register VLR about the Mobile Station MS.
In addition, the Base Station Sub-System BSS corresponds to physical equipment providing radio coverage to the above-mentioned cells which are approximately hexagonal geographical regions in FIG. 7. Each Base Station Sub-System BSS contains equipment required to communicate with the Mobile Station MS.
In the digital cellular telecommunication network system there are three types of logical channels: traffic channel, control channel, and cell broadcast channel. The traffic channels are used to transmit user information like speech or data. The control channels are used to transmit control and signalling information. Finally, the cell broadcast channels are used to broadcast user information from a Mobile Services Switching Centre MSC to the Mobile Station MS listening in a given basic cell/basic service area.
Using the architecture of the digital cellular telecommunication network system outlined above, there may be provided a group of communication capabilities to the subscribers. The basic telecommunication services provided in the GSM digital cellular telecommunication network system are divided into three main groups: bearer services, teleservices, and supplementary services.
The bearer services give the Mobile Station MS the capacity required to transmit appropriate signals between certain user network interfaces such as data services, alternate speech/data, speech followed by data, clear 3.1 kHz audio service and support of automatic request for retransmission technique for improved error rates.
The teleservices provide the Mobile Station MS with necessary capabilities including terminal equipment functions to communicate with other mobile stations, e.g., short message services, or message handling and storage services.
Finally, supplementary services modify or supplement basic telecommunication services and are provided with or in association with the basic teleservices. Such supplementary services comprise, e.g., number identification services, call offering services, call completion services, multi party services, or call restriction services.
In order to be able to deliver an incoming call to a mobile station on the basis of these different services it is necessary to know the location of the Mobile Station MS at any time. This is achieved through continuous data exchange between the Mobile Station MS and the base station sub-system BSS in the service area where the mobile station is located. Thus, the digital cellular telecommunication network system keeps track of the Mobile Station MS and stores location information in the respective Home Location Register HLR and Visitor Location Register VLR.
However, an important fact in the context of location information in PLMN service areas is that the different granularity levels of location information are not at all stored at any time in any of the different Public Land Mobile Networks PLMN within the overall GSM service area. Any of the Home Location Registers HLR within the Public Land Mobile Network PLMN service areas only knows a subscribers current Mobile Services Switching Centre MSC service area. Neither the location area nor the respective cell ID of any of the mobile stations is available.
Therefore, in case a network operator intends to provide so-called location dependent services he has to rely on one of the following three possibilities:
Firstly, the network operator may broadcast information in a so-called short message service format to all subscribers that currently visit a certain cell within a given mobile services switching centre service area. However, here it is not possible to provide information to a specific mobile station nor is it possible to use location information that is implicitly available but not forwarded to any of the different network nodes HLR/VLR/GMSC.
Secondly, in case the network operator uses information contained in the MSRN of the home location register usually embedded in the numbering plan of the local PTT he may retrieve some location information from these MSRN numbers. However, the information contents with respect to granularity of this information is effectively low and varies to a large extent between the different network providers.
Finally, a network operator might consider the use of location numbers, e.g., of existing proprietary solutions for the provision of operator-specific location dependent services. Here, a network operator may define so-called location numbers in dependence of the used equipment where a location number may cover one to several cells within one or several location areas. The current location number of a mobile station may then be retrieved from the Home Location Register HLR in order to provide location dependent services. Besides the fact that here, too, the granularity of information varies a lot in dependence of the number of location areas covered by a single location number another disadvantage of this approach stems from the non-portability of services provided by different network operators.
Therefore, with respect to the state of the art there arises the problem that within the GSM service area and the different sub-service areas and related network nodes covered thereby, location information with respect to Mobile Stations MS of high significance is not necessarily available at all. However, in case a network operator wants to provide a location dependent service it is necessary to have this information within the network node, e.g. such as a Home Location Register HLR or a Visitor Location Register VLR, where the application executing the services is executed.
In addition, although paging is performed within a whole location area (i.e. a number of cells), the cell identifier can be retrieved from the paging response sent by the Mobile Station (compare ETS GSM 08.08 TS/SMG 030808QR1, MSC-BSS interface Layer 3). This possible solution fails however in case of an established call. In that case the cell identifier is transmitted to the MSC but the information is not updated when handovers take place. Furthermore, using a page request just to retrieve location information might cause interference with the usual behaviour of the mobile station or the user's reception.
Still further, the location information available in the Mobile Station could also be transmitted to the NSS by means of the SM Service. As the related messages pass the Short Message Centre which is outside the borders of GSM no time guarantees can be given for the transmission of short messages and thus the transmission channel cannot be used for a realtime service. Location dependent services as introduced above might however have realtime demands if they for example support the determination of call routing.